Audio [Q] Poor sound quality SII-CM10.2-Skoda Amundsen BT car kit

Using :
Galaxy SII wth Cyanogenmod 10.2-201312-14
Skoda Octavia built-in Amundsen gps/BT carkit

My SII is paired with my Skoda BT carkit. No issues to pair whatsoever, connects fine everytime, can play music OK, can receive phone calls OK.

However when I make an outgoing call, sound is almost always of very poor quality. It is cracked and very diffcult to understand (people on the other end also have bad quality). I have tried to do the pairing again, no change. Deactivated audio to have only BT headset, no change.

The strange thing is that incoming calls have perfect sound quality. And with stock ROM I never had such problem.

Can anyone help? Thanks !

By the way, tested on an Audi A4 handsfree kit, same result ...